On the map Scientists who study vitamin D can’t help but notice that a host of diseases seem to vary with latitude. Type 1 diabetes, multiple
sclerosis and even some cancers appear to be more common in areas that get less sun — meaning less opportunity for the body to produce vitamin D. The maps above illustrate the apparent link between solar radiation and breast cancer mortality rates.

D is for discord

The IOM panel members acknowledged
all of these findings — and didn’t use any
of them in setting vitamin D recommendations. They were very forthcoming
about why.

“ We looked extensively at those areas,”Brannon says. In non-bone research, shesays, “we found very limited randomizedcontrolled trials, and evidence for causeand effect was not present.”Some studies did get special note.Hollis’ trial in pregnant women is inter-esting but had yet to appear in a peer-reviewed journal, Brannon says, so itwasn’t used in setting the recommen-dations. The Nebraska cancer study wasdiscounted because the most convincing

Aging brain Studies have shown a link
between vitamin D blood levels and some
age-related disorders. The chart below shows
that parkinson’s patients more often have
lower levels than healthy controls.

finding used only three of the four
trial years, says panel member JoAnn
Manson, an endocrinologist and epidemiologist at Harvard Medical School.
She says the full scope of a trial is the
only fair measure and that secondary
analyses lack credence.

Two large randomized controlled trials are now getting under way and will
provide new evidence.

Physician Carlos Camargo of Harvard
Medical School and colleagues at the University of Auckland are randomly assigning 5,100 older adults in New Zealand to
get a monthly pill containing either a placebo or 100,000 IU of vitamin D — equal
to about 3,300 IU a day. The trial will
assess heart disease, infections and fractures. “It’s a high enough dose to get most
participants up to 35 to 40 nanograms per
milliliter, which is where we think we’ll
find optimum benefits,” Camargo says.

Manson is leading a U.S. trial in
which 20,000 people age 60 and older
are being randomly assigned to get
2,000 IU a day or a placebo. Some will
also get omega- 3 fatty acids. Since they
don’t know what they are getting, participants are allowed to take vitamin D
supplements up to 800 IU daily on their
own. Researchers will measure heart
disease, cancer and stroke among the
participants.

Manson says she hopes the trial “will
provide important information about
the balance of benefits and risks” of
vitamin D.

Whatever the results, though, thesetwo trials may not settle the question.A randomized trial is only as good as itsdesign, Cannell says. Giving people hugedoses of vitamin D once a month cre-ates unnatural swings in the body. “Ourancestors didn’t get one day of sun then29 days without it,” he says.